JP2007047513A - Imaging lens and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens wherein various aberration is satisfactorily corrected, and which attains high optical performance while attaining the miniaturization and the thickness reduction, and also, to provide an imaging apparatus equipped with the imaging lens. <P>SOLUTION: The imaging lens includes, in order from an object side to an image side, an aperture diaphragm S, a first lens L1 having positive refractive power, a second lens L2 having negative refractive power, and a third lens L3 having negative refractive power, and at least one of the surfaces of the first and third lenses is aspherical. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging lens suitable for use in combination with an imaging element and an imaging apparatus having the imaging lens.

  2. Description of the Related Art Conventionally, various information devices including an imaging device configured using an imaging device such as a solid-state imaging device have been proposed. Such an information device is configured as, for example, a so-called digital camera or camera-equipped mobile phone device. An image pickup apparatus used in such information equipment includes an image pickup element and an image pickup lens that forms an image of an object (subject) on an image pickup surface of the image pickup element.

  In this imaging apparatus, as the number of pixels in the imaging element is increased and the density is increased, the imaging lens is required to have high optical performance including high resolution.

  In addition, in an imaging device used in a small information device particularly suitable for carrying, or an information device having a small internal installation space, the imaging lens must be reduced in size and thickness. Become.

  Thus, in order to realize an imaging lens that has high optical performance and is reduced in size and thickness, a three-lens configuration is employed rather than a two-lens configuration. It is known to be promising. It is also known that high optical performance can be maintained by appropriately adopting a lens having an aspherical surface. For example, Patent Document 1 describes a three-lens imaging lens having a positive-negative-negative refractive power arrangement in order from the object side to the image side. A three-lens imaging lens having a positive-negative-negative refractive power arrangement is described in order from the side toward the image side.

Japanese Patent No. 3594088 JP 2004-226487 A

  However, in the imaging lenses described in Patent Document 1 and Patent Document 2, it is difficult to realize optical specifications and high optical performance that have been required in recent years.

  That is, in the imaging lenses described in Patent Document 1 and Patent Document 2, various aberrations, particularly axial chromatic aberration, lateral chromatic aberration, and coma aberration remain, so that the image height is an actual size, for example, When the lens shape is similarly enlarged in accordance with the maximum image height of 3 mm (3 mm is equivalent to the diagonal of the 1/3 type image sensor), the required spatial frequency, for example, 85 lp / mm, (85 lp / mm is the 1/3 type) A sufficient contrast with respect to a frequency of 1/2 of the Nyquist frequency of a 2 million pixel image pickup device is not obtained.

  Therefore, the present invention is proposed in view of the above-described problems, and various aberrations are corrected well, and the required optical specifications and high optical performance are realized while achieving miniaturization and thinning. It is an object of the present invention to provide an imaging lens that can be used and an imaging apparatus having such an imaging lens.

  In order to solve the above-described problems, an imaging lens according to the present invention has the following configuration.

[Configuration 1]
An aperture stop, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a negative refractive power are arranged in order from the object side to the image side. At least one surface of the first lens to the third lens is an aspherical surface.

Imaging lens.

  The expression of refractive power is based on paraxial curvature.

[Configuration 2]
The imaging lens having configuration 1 is characterized in that the first lens has a biconvex shape and the second lens has a meniscus shape with a concave surface facing the object side.

  In addition, the expression of the unevenness of the surface shape is based on the paraxial curvature.

[Configuration 3]
In the imaging lens having Configuration 1 or Configuration 2, when the distance from the aperture stop to the image side surface of the third lens and the total back focus are L, and the focal length of the entire imaging lens system is f, the following conditions are satisfied. The expression (1) is satisfied.
L / f <1.2 (1)

[Configuration 4]
In the imaging lens having Configuration 1 or Configuration 2, when the distance from the aperture stop to the image side surface of the third lens and the total back focus are L, and the focal length of the entire imaging lens system is f, the following conditions are satisfied. The expression (2) is satisfied.
L / f <1.15 (2)

[Configuration 5]
In the imaging lens having any one of Configurations 1 to 3, when the Abbe number of the first lens is νd1, the following conditional expression (3) is satisfied.
νd1> 60 (3)

[Configuration 6]
In the imaging lens having any one of Configurations 1 to 5, the following conditional expression (4) is satisfied when the refractive index at the d-line of the first lens is nd1 and the Abbe number of the first lens is νd1. It is characterized by this.
100 / {(nd1-1) · νd1} <3.3 (4)

[Configuration 7]
An imaging apparatus according to the present invention includes an imaging lens having any one of Configurations 1 to 6, and an imaging device having an imaging surface arranged on an image plane of the imaging lens. is there.

  The present invention can provide a small imaging lens having the above [Configuration 1] or [Configuration 2], which is bright, has a wide angle of view, and has various aberrations corrected satisfactorily. This imaging lens has an optical performance suitable for use in combination with a small imaging device with a high pixel density and high density.

  Furthermore, this invention can provide a small imaging lens having a small overall length of the imaging lens by having [Configuration 3] or [Configuration 4].

  And this invention can correct | amend various aberrations more favorably by having [Configuration 5] or [Configuration 6]. In particular, it is possible to provide a small imaging lens that is brighter, has a wide angle of view, and has a high resolution by satisfactorily correcting axial and magnification chromatic aberration.

  In addition, the present invention has [Configuration 7], so that the imaging lens is small and various aberrations are favorably corrected, and the solid-state imaging with high pixel density and high density as the imaging element. By using the element, a small-sized and high-performance imaging device can be provided.

  That is, the present invention corrects various aberrations and achieves the required optical specifications and high optical performance while achieving miniaturization and thinning, and an imaging lens having such an imaging lens. An apparatus can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  1, FIG. 3, FIG. 5, FIG. 7 and FIG. 9 are cross-sectional views showing the configuration of the imaging lens in Examples 1 to 5 of the present invention.

  As shown in FIGS. 1, 3, 5, 7, and 9, the taking lens according to the present invention has an aperture stop S, a biconvex lens having a positive refractive power in order from the object side to the image side. A first lens L1 having a shape, a second lens L2 having a negative refractive power and a meniscus shape having a concave surface facing the object side, and a third lens L3 having a negative refractive power are arranged. .

  For example, an image pickup surface of an image pickup element is disposed on the image plane of the image pickup lens. As described above, the imaging device is configured by the imaging lens and the imaging element in which the imaging surface is positioned on the image plane of the imaging lens.

  In this imaging apparatus, a filter 1 made of a plane-parallel plate is disposed between the third lens L3 of the imaging lens and the image plane. The filter 1 is a wavelength selection filter for preventing an unnecessary wavelength band from entering the image sensor, a low-pass filter for preventing the occurrence of moire fringes, a cover glass of the image sensor, or the like. Or, they are arranged in combination. In addition, when arrange | positioning combining these various filters as the filter 1, you may arrange | position each filter through the air layer mutually, and may arrange | position each filter mutually joined.

  In this imaging lens, the first lens L1 has a positive refractive power, and by appropriately increasing the refractive power of the first lens L1, the entire length of the imaging lens can be reduced.

  Further, the first lens L1 has a relatively large positive refractive power in order to share the positive refractive power of the imaging lens and to reduce the overall length of the imaging lens. Although it is disadvantageous for aberration correction that a specific lens has a large refractive power, by making the first lens L1 a biconvex shape, the positive surface of the first lens L1 is made by the object side surface and the image side surface. Since the refractive power can be shared, the refractive power of each surface does not become too large. Moreover, it is preferable from the point of error sensitivity to share positive refractive power in each surface.

  In addition, the second lens L2 and the third lens L3 have negative refractive power, and by appropriately increasing the refractive power of the second lens L2 and the third lens L3, the total length of the imaging lens is reduced. can do.

  Further, since the second lens L2 has a meniscus shape with the concave surface facing the object side, off-axis aberrations, particularly coma aberration, are corrected more satisfactorily.

  Further, in order to correct various aberrations satisfactorily, it is preferable that at least one of the first to third lenses L1, L2, and L3 is preferably an aspherical surface.

Further, in this imaging lens, in order to reduce the total length of the imaging lens, the total length of the imaging lens, that is, the distance from the aperture stop S to the image side surface of the third lens L3 and the back focus is set to L. When the focal length of the system is f, it is desirable that the following conditional expression (1) is satisfied.
L / f <1.2 (1)

In this imaging lens, it is more preferable that the following conditional expression (2) is satisfied.
L / f <1.15 (2)

Furthermore, in this imaging lens, in order to correct various aberrations, particularly axial and magnification chromatic aberration, when the Abbe number of the first lens L1 is νd1, the following conditional expression (3) is satisfied. It is desirable that Conditional expression (3) is satisfied when the optical material of the first lens has low dispersion.
νd1> 60 (3)

As another notation, in this imaging lens, in order to better correct various aberrations, particularly axial and magnification chromatic aberration, the refractive index at the d-line of the first lens L1 is nd1, the first lens When the Abbe number of νd1 is νd1, it is desirable that the following conditional expression (4) is satisfied. Conditional expression (4) is satisfied when the optical material of the first lens has low dispersion with respect to its refractive index.
100 / {(nd1-1) · νd1} <3.3 (4)

  In this imaging lens, an appropriate optical material such as a synthetic resin material (plastic) or glass can be used as a material forming the first to third lenses L1, L2, and L3. For example, as the optical constants of the materials of these lenses L1, L2, and L3, the refractive index Nd at the d-line (wavelength 587.6 nm) is 1.4 to 2.1, and the Abbe number νd at the d-line is 20 to 85. The thing of the range of is preferable. Further, as materials of these lenses L1, L2 and L3, those having a refractive index Nd of 1.45 to 1.9 and an Abbe number νd of 20 to 70 from the viewpoint of availability and manufacturing cost. Is more preferable.

  For the first lens L1, for example, by using low-dispersion glass having an Abbe number νd of about 60 to 85 in the d-line, axial and magnification chromatic aberration can be corrected well. By using such a low-dispersion glass material and performing molding using a molding die, the shape of each optical surface can be aspherical, and various aberrations can be corrected more favorably.

  For the first lens L1, the required refractive power can be obtained without excessively increasing the curvature of each surface by using a glass material having a high refractive index with a refractive index Nd of about 1.6 to 2.0 at the d-line. Can be obtained. By using such a high refractive index glass material, if the curvature of each surface of the first lens L1 is not excessively increased, molding processing and molding using this molding die can be facilitated. it can.

  For the second lens L2, for example, chromatic aberration can be favorably corrected by using a low dispersion material having an Abbe number νd of about 35 or less in the d-line.

  The first to third lenses L1, L2, and L3 can be molded by a precision mold press. If the first to third lenses L1, L2, and L3 are molded by a precision mold press, when the lenses L1, L2, and L3 are molded, the shift amount between the first surface and the second surface of each lens is 10 μm or less, The inclination of the axis between the first surface and the second surface (molding tilt) can be made within 2 minutes, and an imaging lens having high imaging performance can be configured.

  Hereinafter, the present invention will be specifically described by giving examples according to the present invention. In addition, this invention is not limited to the structure of these Examples.

The symbols used in the following description of each example are as follows.
R: radius of curvature of refracting surface [mm]
D: Distance between top surfaces of refractive surfaces [mm]
Nd: Refractive index of lens material at d-line νd: Abbe number of lens material at d-line f: Focal length of entire lens system [mm]
F: F number 2Y: Image size (Y: Maximum image height) [mm]

The shape of the aspherical surface is represented by the following aspherical expression in an orthogonal coordinate system in which the intersection of the surface and the optical axis is the origin and the optical axis direction is the Z axis.
Z = Ch ² / [1 + √ {1- (1 + K) C 2 h 2} ] ^{+ A6h 4 + A6h 6 + A8h} 8 + A10h 10 + A12h 12 + A14h 14

However, symbols in this aspherical expression are as follows.
h = √ (X ² + Y ² )
C: Paraxial curvature (C = 1 / R)
K: Conic constant A4 to A14: 4th to 14th aspheric coefficients

[Example 1]
The lens data in Example 1 of the present invention is shown in [Table 1] below.

  The imaging lens has a focal length of 4.90 mm, an F number of 3.35, and a maximum image height of 3.0 mm.

In the imaging lens according to the first embodiment, the following relationship is established.
L / f = 1.18
νd1 = 64.17
nd1 = 1.517
100 / {(nd1-1) · νd1} = 3.01

  That is, conditional expression (1), conditional expressions (3) and (4) are satisfied.

  FIG. 1 is a cross-sectional view illustrating a configuration of an imaging lens according to Embodiment 1 of the present invention.

  2A and 2B are aberration diagrams of the imaging lens according to Example 1 of the present invention. FIG. 2A shows astigmatism (“×” indicates sagittal, “+” indicates meridional), and FIG. 2B indicates spherical aberration (“ “+” Indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), “□” indicates C-line (656.3 nm)), (c) indicates distortion, (d) Indicates meridional coma aberration (“+” indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), and “□” indicates C-line (656.3 nm)).

  In the imaging lens according to the first embodiment, as shown in FIG. 2, various aberrations are corrected favorably, and it is suitable as an imaging lens constituting a small and thin imaging device in combination with a small imaging device having high resolution. is there.

[Example 2]
Lens data in Example 2 of the present invention is shown in [Table 2] below.

  The imaging lens has a focal length of 4.63 mm, an F number of 3.1, and a maximum image height of 3.0 mm.

In the imaging lens according to the second embodiment, the following relationship is established.
L / f = 1.14
νd1 = 64.17
nd1 = 1.517
100 / {(nd1-1) · νd1} = 3.01

  That is, conditional expressions (1) to (4) are satisfied.

  FIG. 3 is a cross-sectional view illustrating a configuration of an imaging lens according to Example 2 of the present invention.

  4A and 4B are aberration diagrams of the imaging lens according to Example 2 of the present invention. FIG. 4A shows astigmatism (“×” is sagittal, “+” is meridional), and FIG. 4B shows spherical aberration (“ “+” Indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), “□” indicates C-line (656.3 nm)), (c) indicates distortion, (d) Indicates meridional coma aberration (“+” indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), and “□” indicates C-line (656.3 nm)).

  In the imaging lens in Example 2, various aberrations are favorably corrected as shown in FIG. 4, and the imaging lens is suitable as an imaging lens constituting an imaging apparatus in combination with an imaging element.

Example 3
Lens data in Example 3 of the present invention is shown in [Table 3] below.

  The imaging lens has a focal length of 4.90 mm, an F number of 2.8, and a maximum image height of 3.0 mm.

In the imaging lens according to Example 3, the following relationship is established.
L / f = 1.18
νd1 = 67.20
nd1 = 1.582
100 / {(nd1-1) · νd1} = 2.51

  That is, conditional expression (1), conditional expressions (3) and (4) are satisfied.

  FIG. 5 is a cross-sectional view illustrating the configuration of the imaging lens according to Example 3 of the present invention.

  6A and 6B are aberration diagrams of the imaging lens according to Example 3 of the present invention. FIG. 6A shows astigmatism (“×” indicates sagittal, “+” indicates meridional), and FIG. 6B indicates spherical aberration (“ “+” Indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), “□” indicates C-line (656.3 nm)), (c) indicates distortion, (d) Indicates meridional coma aberration (“+” indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), and “□” indicates C-line (656.3 nm)).

  In the imaging lens according to the third embodiment, various aberrations are favorably corrected as shown in FIG. 6, and the imaging lens is suitable as an imaging lens constituting an imaging apparatus in combination with an imaging element.

Example 4
Lens data in Example 4 of the present invention is shown in [Table 4] below.

  The imaging lens has a focal length of 4.90 mm, an F number of 3.5, and a maximum image height of 3.0 mm.

In the imaging lens according to Example 4, the following relationship is established.
L / f = 1.17
νd1 = 64.17
nd1 = 1.517
100 / {(nd1-1) · νd1} = 3.01

  That is, conditional expression (1), conditional expressions (3) and (4) are satisfied.

  FIG. 7 is a cross-sectional view illustrating a configuration of an imaging lens according to Example 4 of the present invention.

  8A and 8B are aberration diagrams of the imaging lens according to Example 4 of the present invention. FIG. 8A shows astigmatism (“×” is sagittal, “+” is meridional), and FIG. 8B shows spherical aberration (“ “+” Indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), “□” indicates C-line (656.3 nm)), (c) indicates distortion, (d) Indicates meridional coma aberration (“+” indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), and “□” indicates C-line (656.3 nm)).

  In the imaging lens in Example 4, various aberrations are favorably corrected as shown in FIG. 8, and it is suitable as an imaging lens constituting an imaging apparatus in combination with an imaging element.

Example 5
Lens data in Example 5 of the present invention is shown in [Table 5] below.

  This imaging lens has a focal length of 4.60 mm, an F number of 3.0, and a maximum image height of 3.0 mm.

In the imaging lens according to the fifth embodiment, the following relationship is established.
L / f = 1.13
νd1 = 67.20
nd1 = 1.582
100 / {(nd1-1) · νd1} = 2.51

  That is, conditional expressions (1) to (4) are satisfied.

  FIG. 9 is a cross-sectional view illustrating a configuration of an imaging lens according to Example 5 of the present invention.

  10A and 10B are aberration diagrams of the imaging lens according to Example 5 of the present invention. FIG. 10A shows astigmatism (“×” is sagittal, “+” is meridional), and FIG. 10B shows spherical aberration (“ “+” Indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), “□” indicates C-line (656.3 nm)), (c) indicates distortion, (d) Indicates meridional coma aberration (“+” indicates d-line (587.6 nm), “Δ” indicates F-line (486.1 nm), and “□” indicates C-line (656.3 nm)).

  In the imaging lens in Example 5, various aberrations are satisfactorily corrected as shown in FIG. 10, and it is suitable as an imaging lens constituting an imaging apparatus in combination with an imaging element.

It is sectional drawing which shows the structure of the imaging lens in Example 1 of this invention. FIG. 5 is an aberration diagram (astigmatism, spherical aberration, distortion, and meridional coma) of the imaging lens according to Example 1 of the present invention. It is sectional drawing which shows the structure of the imaging lens in Example 2 of this invention. FIG. 6 is an aberration diagram (astigmatism, spherical aberration, distortion, and meridional coma) of the imaging lens according to Example 2 of the present invention. It is sectional drawing which shows the structure of the imaging lens in Example 3 of this invention. It is an aberration diagram (astigmatism, spherical aberration, distortion aberration and meridional coma aberration) of the imaging lens in Example 3 of the present invention. It is sectional drawing which shows the structure of the imaging lens in Example 4 of this invention. It is an aberration diagram (astigmatism, spherical aberration, distortion aberration, and meridional coma aberration) of the imaging lens in Example 4 of the present invention. It is sectional drawing which shows the structure of the imaging lens in Example 5 of this invention. It is an aberration diagram (astigmatism, spherical aberration, distortion aberration, and meridional coma aberration) of the imaging lens in Example 5 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Filter S Aperture stop L1 1st lens L2 2nd lens L3 3rd lens

Claims (7)

An aperture stop, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a negative refractive power are arranged in order from the object side to the image side. ,
An imaging lens, wherein at least one surface of the first lens to the third lens is an aspheric surface. The first lens has a biconvex shape;
The imaging lens according to claim 1, wherein the second lens has a meniscus shape with a concave surface facing the object side. When the distance from the aperture stop to the image side surface of the third lens and the back focus is L and the focal length of the entire imaging lens system is f, the following conditional expression (1) is satisfied. The imaging lens according to claim 1, wherein:
L / f <1.2 (1) When the distance from the aperture stop to the image side surface of the third lens and the back focus is L and the focal length of the entire imaging lens is f, the following conditional expression (2) is satisfied. The imaging lens according to claim 1, wherein:
L / f <1.15 (2) The imaging lens according to any one of claims 1 to 3, wherein when the Abbe number of the first lens is νd1, the following conditional expression (3) is satisfied.
νd1> 60 (3) The following conditional expression (4) is satisfied, where nd1 is the refractive index of the first lens at the d-line, and νd1 is the Abbe number of the first lens. The imaging lens according to any one of the above.
100 / {(nd1-1) · νd1} <3.3 (4) The imaging lens according to any one of claims 1 to 6,
An imaging device comprising: an imaging device having an imaging surface arranged on an image surface of the imaging lens.